If anyone had told me three months ago that a company was going to propose a system that would fully disable GPS in areas that cover most of the population of the US, I would have ignored them. If someone told me two months ago that the FCC would give this proposal serious consideration, I would have laughed. If someone had told me a month ago that the US Federal Communications Commission would actually approve this scheme, I would have considered them crazy. And yet, that’s exactly what’s happened; the FCC has given conditional approval to LightSquared’s 4G LTE proposal (PDF link) . If implemented as planned, all current GPS receivers will no longer operate correctly in areas covered by their system, which include the overwhelming majority of the US population. I wish I were kidding, but I’m not. There’s a lot of technical jargon used in discussing this issue, so in this post I thought I’d try to explain the issues with a somewhat less technical, and hopefully more accessible approach. Technical nitpickers may see some oversimplification, for which I apologize … not at all.

At their most basic level, GPS receivers are pretty close to FM radios. So to explain some of these principal issues behind the GPS problem in understandable terms, I’ll use the basics of FM radio broadcasting. To tune in an FM radio station, you turn your radio’s dial or push the buttons until the receiving frequency of the radio is set to that of the station: 89.5, 101.7, 104.1, and so on. Those numbers refer to the number of cycles per second of the frequency in millions, so that 101.7 is a radio signal operating at 101.7 million cycles per second, abbreviated as 101.7 MegaHertz (MHz) for short. But that’s just the main frequency, sometimes referred to as the central “carrier wave”; receiving a signal at just at frequency wouldn’t give you any signal information, like music/talk/news. To encode that signal, the frequency of that carrier wave is varied, or “modulated”, by the signal; your radio then monitors those variations in frequency around the central carrier wave’s frequency, and then converts them back to the original signal, music/talk/news. Frequency being modulated = Frequency Modulation = FM.

If you had two stations broadcasting in the same area on the same frequency, they would interfere with each other, making both of them unlistenable. If the frequency is only slightly different, they will also interfere with each other. To prevent this, the FCC licenses broadcasters to transmit on a specific frequency, and also makes sure that the frequencies are far enough apart so that one station’s broadcasts won’t interfere with another station. In the original days of FM, the minimum spacing for FM frequencies was 800 thousand cycles per second (800 KiloHertz or KHz, 0.8 MHz); so if one station was at 90.1 MHz, the closest frequencies allowable to that station would be 89.3 MHz and 90.9 MHz, offset 0.8 MHz up and down from the center one.

With time, the FCC has loosened that frequency spacing requirement up a bit, taking into account factors like improved FM radio technology, the broadcast power of the station, and the distance from other stations assigned the same frequency. For the most part, the system works, but you’ve probably experienced occasions when you’ve been listening to one FM station, only to have a second signal cut in and interfere with the first station’s signal. This is especially noticeable if you drive right by an FM radio broadcast antenna; the signal from that station can be so strong, it wipes out reception from any stations that are even marginally close to it in frequency. Because a station requires about 150 KHz of frequency modulation bandwidth to carry its signal, the FCC has also mandated that all standard FM tuning signals need to be at least 200 KHz apart; that’s why your FM tuner jumps from 100.1 to 100.3 to 100.5, bypassing 100.2, 100.4; those frequencies need to be kept free to make sure stations don’t “step” on each other’s signals.

OK, so back to GPS. While GPS doesn’t technically use frequency modulation, it uses a closely-related system called “phase modulation“, which also relies on a carrier wave. The main signal broadcast by GPS satellites, and used by the overwhelming majority of GPS receivers for determing position, is the “L1” frequency, with the carrier wave 1.57542 billion cycles per second (aka a GigaHertz, or GHz); including the total frequency band required for phase modulation, the range is 1.559 GHz to 1.610 GHz. Phase modulation is used to transmit digital information with pulses 1-millionth of a second wide from the satellites to your GPS receiver; the receiver takes this data from multiple satellites, and uses it to calculate your position. This frequency was defined in the late 1970s, and has been used continuously for GPS operations since the system went operation early in the 1990s, twenty years now. This frequency band is also part of a larger range of frequencies designated for use in satellite broadcasting. As with FM radio, you need to separate the frequency bands far enough apart so that the signals don’t interfere with each other; you also need to make sure that a signal at one frequency isn’t broadcast at such a high power that it will interfere with signals broadcast at neighboring frequencies. The latter isn’t usually a problem – the signal strength from satellites 12,000 or 23,000 miles above the earth is usually so low that interference between adjacent frequency bands is infrequent.

So, enter LightSquared. LightSquared wants to build a high-speed wireless broadband network on the cheap. Problem is, the FCC holds regular auctions for frequency space, with all the big wireless players (Verizon, ATT, Cingular, Google) bidding billions of dollars for this frequency space to carry their traffic; a smaller company like LightSquared can’t compete financially. But LightSquared came up with several clever workarounds to get past this issue. Satellite frequencies are also regulated and auctioned by the FCC, but they usually go for prices far lower than terrestrial frequency space. LightSquared acquired a small satellite company called SkyTerra that already owned frequency rights for 1.525 GHz to 1.559 GHz, directly adjacent to the frequency band designated for GPS. They then announced plans to develop a satellite-based Internet access service using those frequencies. Satellite signals by themselves would be so weak, that Internet speeds would likely be limited to no more than a few megabits per second, comparable to current 3G wireless network speeds. But FCC regulations have a loophole that allows satellite services to broadcast stronger signals terrestrially to supplement satellite coverage in those areas where coverage might be weak. This terrestrial broadcast signal can be as strong as the FCC allows, and is covered by the satellite auction price paid by the licensee.

So LightSquared announces a “satellite Internet access” service, but one supplemented by free use of terrestrial transmitters. But these terrestrial transmitters aren’t intended merely to fill in gaps in satellite coverage; these are high-power transmitters that allow LightSquared to offer the equivalent of 4G wireless Internet speeds (up to 100 Mbps), without paying for terrestrial spectrum. So that’s how LightSquared plans to do high-speed wireless broadband on the cheap – they don’t have to pay for the frequency spectrum they’re using. It’s a clever use of loopholes, and one I wouldn’t have a problem with, except that they will be broadcasting at high-power at a frequency that will interfere with GPS signals to the point that GPS receivers will no longer operate correctly. And this isn’t just a few transmitters – LightSquared’s plans are to install 40,000 transmitters to cover areas that contain most of the US population.

This GPS interference isn’t just a hypothesis. Members of the US GPS Industry Council, Trimble and Garmin met with the FCC on January 19th to present and discuss Garmin’s tests of the LightSquared proposal (PDF link), and its potential for interference with GPS receivers. Garmin used LightSquared’s own proposed transmitter power levels to evaluate the effects of this transmitters on an automotive GPS (Garmin nuvi 265W) and an avionic GPS (GNS430W). Here are screen captures summarizing the effects of the LightSquared transmitters on GPS receiver performance at different distances:

If you get within 0.66 miles of a LightSquared transmitter in open conditions, you’ll lose your position fix with the automotive nuvi 265W, further away in a city environment like New York or Chicago. The results are even worse for the aviation GPS. The FAA has essentially discontinued support for the old LORAN electronic navigation system in favor of GPS, and now LightSquared has proposed a system that essentially disables GPS in exactly the areas aviation needs it most. Garmin’s conclusion, shared by other industry proponents:

The operation of so many high powered transmitters so close in frequency to the GPS operating frequency (1575.42 MHz) will create a disastrous interference problem to GPS receivers to the point where GPS receivers will cease to operate (complete loss of fix) when in the vicinity of these transmitters.

Grant of the LightSquared waiver would create a new interference environment and it is incumbent on the FCC to deal with the resulting interference issues before any interference occurs. Several federal agencies with vital concerns about this spectrum band, including the Departments of Defense, Transportation and Homeland Security, have informed NTIA that they believe the FCC should defer action on the LightSquared waiver until these interference concerns are satisfactorily addressed.

Retrofit current GPS equipment with improved electronics; possible but expensive for high-end equipment, impossible at a reasonable cost for consumer-grade equipment

Replace all current incompatible GPS receivers with new ones that have improved filtering. While the marginal cost increase on a GPS receiver is likely to be low, the requirement that you have to replace the entire unit will make this staggeringly expensive. Every GPS receiver (automotive, aviation, handheld, mobile phone) would need to be replaced.

If it weren’t for its detrimental consequences on GPS, I’d think that LightSquared’s system would be a great idea – high-speed wireless Internet access in most populated places, and lower-speed access anywhere in the world by satellite. And if the FCC wants to propose regulations requiring better frequency band filtering in GPS receivers, and other types of satellite-band-based systems, to allow exactly these kind of systems to be developed in the future, I could get on board with that as well. But it should be up to LightSquared to prove that their system won’t interfere with GPS the way it is right now. GPS is the established system – twenty years of operation, hundreds of millions of receivers, uncountable numbers of applications. If LightSquared interferes with GPS, it should be required either to fix the problem itself, or be denied permission to function. That the FCC would even consider LightSquared’s proposal without modification, much less approve it, is astonishing.

The FCC ideally would regulate the radio spectrum in a way that best suits the needs of the public. Decisions would be made to allocate spectrum based on whether it is in the public need or interest.

Unfortunately, the FCC has not been doing that for decades, at least as long as the cellphone industry has been in existence.

They serve the businesses and decide what frequencies are allocated based on what brings the most profit. They use Frequency auctions as a source of income to the government and who can say how much money is changing hands in the background, either.

This is what is wrong with the FCC and has continued to get worse every year. The radio spectrum belongs to the people, not big businesses. The FCC is supposed to see to it that it is used to provide for the publics needs, not the shareholders.

Frequencies should not be auctioned – sold- to the highest bidder. They cannot be owned, they belong to the people. They are a natural resource. The FCC should grant use of a frequency for the public good, not for money. And grants should be revokeable if the public is no longer being served or someone else will serve them better.

That is what the FCC was originally intended to be, but like most government agencies has become corrupted by big business and money.

In reading the letter (Horbingerletter.pdf) from your link “may have political connections deep inside the current administration”, I noticed the name Michael Falcone in the header of letter as a member of the board.

how come in europe the FM stations are 50 kHz apart and it works great? you can check this on any international radio that can be switched between europe and US – btw it also changes the band delta for MW

This is very similar to the FCC’s experiment with Broadband over Power Line (BPL) that required years of opposition by the American Radio Relay League before it was finally exposed in court as a conspiracy by high level administrators inside the FCC. BPL was shown to be an interference problem to HF services wherever installed, yet the FCC continued to support it against all reasonable technical objections, including their own engineers. The FCC has become a political arm of the administration in power, and has a overzealous desire to get broadband internet service to the masses, for the glory of their political bosses. If you want to know how to fight this, become familiar with the war the ARRL waged with the FCC over the past decade.

Doesn’t the headline and lead overstate things just a bit? At worst, we have a proposal for a system that has the potential to disrupt GPS reception, perhaps in large areas. Now, do you really think the FCC would approve such a system?

While people are right to be concerned about the proposal and how the FCC handles it, this is a long way from being settled. GPS is a very important issue at the Commission, though I am not sure it is actually under FCC regulation (as a military system).

Let’s all breathe normally and see this through. Screamer headlines don’t help.

Screamer headlines aside, David N5FDL, I’d think that you would be sensitive to the BPL issue the FCC allowed to go on for years, in spite of the negative technical assessments of their own engineers. Perhaps you were not personally affected, but many in the Manassas, VA area were. Possibly you are unaware of the modified technical reports, purposely reversing their own engineers’ findings and recommendations (see http://www.arrl.org/news/it-seems-to-us-we-win-in-court ). Based on previous FCC conduct, this is not an experimental study by objective technical experts. The FCC has already demonstrated they have ulterior motives and protection of our electromagnetic resources is NOT their top priority.

I wish I could be as sanguine as you about this. But if you read the full FCC approval, as I have, what it says quite clearly is that LightSquared pretty much has a complete go-ahead to move quickly on implementing this system, to the point where the FCC is pretty much willing to waive many of its standard requirements for such proposals. The GPS issues are relegated to the back pages, and it’s put squarely into LightSquared’s hands to decide whether they’ve been resolved successfully. LightSquared pays for the study, chooses the technical experts, and issues the final report. And the FCC states quite explicitly that they expect the GPS industry to act “in good faith”, while making no such statements about LightSquared. This despite the fact that only the GPS industry has presented representative technical data, and it indicates the serious consequences on GPS reception this system could have. The only data LightSquared has on its side is a study by Qualcomm on the effects of the cellular uplink signal at 1710 MHz on GPS reception, where they show how their filtering system protects GPS from being affected. But …

– The central frequency of this cell signal is 100 MHz away from the GPS signal; the LightSquared signal is 50 MHz, much closer, and far more likely to cause interference;
– Qualcomm says that it doesn’t yet know what the effect of the much stronger downlink signal would be, comparable to transmissions from the LightSquared and whether they could come up with a solution. Translation: There is a problem, and they don’t want to admit that publicly.
– Qualcomm says that have no data on the potential effects of “legacy” systems, which means all current GPS receivers, not just the ones that have their chipsets.

I was unfamiliar with the BPL (broadband over power line) battle until Mike mentioned it in the comments. You really should check out the history of that before assuming that the FCC will make decisions that make sense, both technically and in terms of the greater public good.

Think about it this way. A company proposes a system that could make them a lot of money, but which technically-competent people believe will interfere with GPS to the point of making it inoperable. The opponents present strong technical data that supports their arguments, while the company doesn’t. Do you:

A. Tell the company to come back after they’ve proved that their system won’t have the serious effects that their opponents claim, and require that the testing be done by an unbiased third party;

B. Approve the system, and put the company, with financial incentives in seeing the project go forward, in charge of the process that is supposed to resolve the interference issue. And also imply that the opponents can’t be trusted to act in good faith.

You’d think so; certainly, the DOD and DOT communicated their concerns to the FCC via the NTIA. And yet, the FCC gave the proposal conditional approval. In the case of BPL, they approved it even after evidence was presented that it would interfere with aviation radio frequencies. Final approval of this would be crazy, but just the fact that it’s gotten this far is crazy, too.

Why don’t you put the blame where the blame belongs?
It is not the FCC fault or this new providers fault that Garmin has produced receivers that are sub par.
If you build receivers that lack front end selections and where the IF is as wide as a “”barn door” just because you can get away with it and make a crap load of profit by doing so..does not means it is the FCC or anyone else fault. Garmin always knew that in this world of shrinking resources there would be close neighbors…so, why did they build inferior equipment to start? Because its cheap mass produced and they actually believe they can get away with it by having people stir up the masses and point the finger in the other direction thus causing a consumer uproar and the possibility of lawsuits government interference on they’re behalf and more.

Maybe this all results in new regulation of the consumer industry….one can only hope.

Wanna bet, none of the primary users of this service has ANY problems with the new proposal and service?

You have a fundamental misunderstanding of the situation. GPS frequencies, and most other frequency ranges in the L1 band, were designated for satellite use. This means low-power at the receiver, which in turns means you don’t normally have to worry about crosstalk between adjacent frequencies, since the power level is so low. Terrestrial broadcast at those frequencies was only supposed to be to supplement the satellite broadcasts in areas where it’s blocked by topography or man-made objects, and not for general high-power broadcasts. The FCC waiver for LightSquared allows them to broadcast at much higher powers than any satellite signal would ever be, which is changing the rules midstream. How exactly were GPS manufacturers supposed to anticipate that frequencies intended only for low-power satellite broadcasts would now be allowed to be used by high-power terrestrial transmitters? GPS has operated without issue, and without frequency conflicts, for over twenty years now. LightSquared creates a system that steps over the specified frequency bounds, and you’re blaming the GPS makers for this?

Consider the following hypothetical: the FCC changes their rules to allow one FM broadcaster to transmit at power levels so high, it wipes out the signal from most of the other stations. Would you argue that the FM radio makers are responsible for the problem, since they didn’t anticipate this rule change and engineer their radios for specifications they didn’t know they would have to meet?

If you read the full documents, you’ll see it’s the entire GPS industry that’s up in arms about this, not just Garmin. At the FCC meeting where Garmin presented their results, the US GPS Industry Council was present, as was Trimble. Trimble makes ultra-high-precision GPS receivers and equipment that can cost tens of thousands of dollars, and they are also seriously concerned about this issue. It isn’t a question of Garmin making cheap equipment, it’s the change in allowed signal power levels for a band that was always supposed to be low-power.

Finally, even LightSquared doesn’t know that there’s a way to fix this problem; they say you can filter it out, but they haven’t even proved that yet. Qualcomm, the company that’s making the chipsets for LightSquared, has looked at these issues, and can’t say with certainty that even the GPS on their own chipsets won’t have a problem; see a few comments above for more info.

The GPS system is owned by US Dept of Defence and Im pretty certain that they will not tolerate the deployment of a system that will seriously degrade the utility value of GPS IN THEIR OWN BACK YARD so I bet they will be shaking the trees at the highest level to resolve this.
Next, the USA will stand to lose market share to other sat nav systems eg Galileo (European), Glonass (Russia) or Compass (China). This will spur accelerated deployment of such systems and seriously impact on USA manufacturing.

Then perhaps this is a ploy to make existing GPS gesr redundant and spur another round of GPS components design and distribution and prod a whole replacement market. Stupid idea as only the USA will be affected. Again this will spur deployment of alternative systems to the detriment of US interests on American home soil.

But the biggest consequence will be the USA losing control of the global users of navigation aids.
But this seems inevitable anyway

Paul Cone, the military (and from my knowledge commercial airlines too) uses the L2 band. That is a different frequency (around 1200MHz). The signals on it are encrypted and thus not available for normal users.

I believe that the military uses the L1 signal as the primary source; L2 is strictly to improve accuracy. It’s encrypted, but the coding was cracked a while back, and some commercial GPS equipment makers use it to improve accuracy (dual-frequency GPS receivers). But the cracking takes some time, so it’s not practical for real-time position information, as would be necessary for aviation use. Standard GPS with WAAS is considered acceptable for most aviation navigation functions.

Out in the Gulf, away from populated areas that would have these transmitters, GPS will continue to work perfectly fine. It’s only those areas in range of the transmitters that will have problems with interference.

LightSquared has procured political favor with the current administration (41 thousand dollars worth), and a political appointee (FCC chair) has subverted the very process that the FCC is supposed to uphold.

Buckle up folks. Very soon now we will all need to throw out our existing GPS receivers and buy all new ones. The proper way to handle this would have been a 5 to 10 year phase out of old receivers through natural attrition before the interfering transmitters were permitted to go online. You and I are footing the bill on this one so that a handful of wealthy well connected people can make billions.

Please note that no one has “cracked” the P(Y) code transmitted on L2. Commercial dual frequency receivers track the L2 carrier phase. This can and is done without having to decode the P(Y) code. They do not decode the P(Y) code nor do they need to. Only military dual frequency receivers with keys loaded can decode and utilize the P(Y) code.

Had you contacted us before running your article, we would have been glad to help you with the facts. First, and most important, like all spectrum holders we have an obligation to operate properly within our band, and we take that responsibility very seriously. To suggest otherwise is a disservice not only to us, but also to your readers.

In an open and transparent process, the FCC has granted LightSquared‘s request to create a network capable of satellite and terrestrial wireless communication across the U.S. Millions of Americans have no access to high-speed broadband, and, in the spirit of The National Broadband Plan, we will be able to bring nationwide, seamless coverage.

In preparation of this service, we are working collaboratively with the FCC, federal spectrum holders and the GPS community to ensure that the technologies can co-exist. A Technical Working Group has been formed, and this Technical Working Group will submit monthly reports to the FCC articulating the progress. We will launch operations in our band only when this process is completed to the satisfaction of the government.

I would also like to point out that the Garmin tests that you refer to were not made under appropriate circumstances so the results are not accurate indications of how our network will perform. To get a real examination of the situation, tests must be conducted in the proper band and with the right filters. We’re now engaging in testing supported by the government and being done with the cooperation of many in the GPS community. We believe that this process will produce the most reliable results and will show that our network and GPS can coexist.

We have committed to the FCC that by 2015, we will bring 4G wireless broadband to 92 percent of America, enabling critical and reliable communication to consumers, businesses, public safety workers and other government entities. We are investing billions to ensure this is done efficiently and safely.

Ms. Schaefer, your comment is a classic piece of PR hackery. Representatives from the GPS industry, telecommunications industry and the government have all raised serious concerns about the interference your system could create, and your response is we’re looking into it, and we’ll figure something out. The onus should be on you to prove that your system won’t create interference, and make any approval of your system contingent on that – not grant conditional approval on your vague assurances that you think you can make things work.

You devote most of your comment to extolling the potential benefits of your system. If your system didn’t have the potential to disrupt GPS and military communications, I’d be 100% behind it. But it does, and unless you can offer solid proof upfront that you can implement it without affecting all currently operating equipment, the costs far outweigh the benefits.

Finally, you badmouth the Garmin results. Unless you have technical expertise in this matter, you are simply parroting your company line. And even if you have technical expertise, I would expect two links at a minimum to back up your position:

– A link to your technical response to Garmin’s test. Sorry, but your statement that the tests weren’t made “under appropriate conditions” isn’t good enough.

– A link to your own tests that show your system won’t affect GPS reception, under realistic conditions (i.e. Qualcomm’s tests don’t count, since they’re not done under realistic conditions (not the same frequency, uplink interference only analyze)).

If you can’t provide links to both of those, then let me set the record straight: you’re full of crap, and I will continue to point that out at every opportunity.

This is a big deal. I have been concerned with the technical competence of the FCC for some time. When the BPL fiasco started my thoughts were how could any technically competent person know that this was a good way to go? It was obviously an attempt to provide a tertiary path for internet connectivity. While laudable for competition it was a failure technically, and became the equivalent of legislating the value of pi. You cannot change the laws of physics in Congress or the FCC. There were obvious political overtones in the BPL attempt, the depth of which are not known.

One has to assume that this situation will be similar to BPL. The FCC will allow a few pilot systems, GPS receivers will fail, the users will scream, and the FCC will push it under the rug hoping no one notices. Unfortunately for the FCC, they will take out the public’s GPS access, and the screams will be louder than what the Amateur Radio Service could bring on. An average reporter will be able to demonstrate the effects with ease. There will be no way to spin this in a positive way.

So will it happen? Yes the FCC will blindly launch a pilot program. That program will wipe out GPS for the average user, and the screaming will put the lawyer bureaucrats into scramble mode to fix it. Unfortunately, it will be the public that suffers.

The FCC, like many other Federal agencies that directly serve the public, is required by law to recover some of its costs from user fees. For details, see 31 U.S.C. 9701, and Office of Management and Budget Circular A-25. (http://www.whitehouse.gov/omb/circulars_a025/) The amount of fees collected ranges from 13% of operating cost to 129% of operating cost (FY 1996 figures, the most recent I can quickly find. http://www.ers.usda.gov/publications/aer775/aer775c.pdf) In that year, the FCC recovered 73% of its operating cost in user fees. If you have a problem with that (like auctioning the RF spectrum) then complain to your congresspeople.

The GPS system, originally the military NAVSTAR system, has been in operation since the late 1970s. (The first Block I satellite was launched in 1978.) In 1983, after the KAL Flight 007 shootdown, President Reagan directed that the GPS system be freely accessible by civilians. The first satellite specifically designed for civilian as well as military use was launched in 1989.

The GPS system has a capability called Selective Availability (SA). When SA is on, position accuracy is no better than ± 100 m. Military receivers can filter out the SA interference, and modern ones have access to an encrypted signal as well. In 1996, President Clinton continued Reagan’s mandate that the GPS system be a freely accessible dual-use system. As a direct result, SA was turned off on May 1, 2000. That improves basic position accuracy to ± 20 m. (BTW, the computed position is the center of a sphere, not a circle – and it is relative to a geodesic model of the Earth, not the true surface.)

The GLONASS and GALILEO systems will operate in the SAME frequency bands as the US GPS system – which means they will be jammed just as much as GPS will.

There are MANY users of the GPS system – not just military and other users of commercial navigation devices. All of these will be severely impacted by any interference with GPS signals. Cell phones are required to have GPS receivers, so they can be located by emergency responders and law enforcement. (I recently heard that there are over 300 million cell phones in the US – almost one for each person!) Commercial aviation (passenger airlines and air freight carriers) and general aviation (business and private aircraft) use GPS systems for navigation – the FAA is actively working to permit navigation by GPS only, instead of the airways system that was developed in the 1920s and 1930s. Many land surveyors now use instruments with GPS receivers. Truck lines and other vehicle fleets have GPS receivers in the vehicles that allow tracking by the owner. Many companies use the same system to keep track of other mobile capital assets. (You can buy a system to keep track of your teenager!) Many organizations use GPS-disciplined frequency standards. This includes calibration laboratories, scientific research establishments, computer network and internet service providers, telecommunications companies, financial markets, and anyone else that requires precise timing or frequency standards. (Navigation requires time measurement from three or more satellites. The system can derive either position – for most users – or precise time and time interval. The inverse of time interval, of course, is frequency.) Even the LORAN system, operated by the Coast Guard, is actually now GPS-based because it uses GPS-disciplined frequency standards.

And the list of impacted people and organizations can go on even longer – but not here & now.

I think GPS used as a timing source needs more attention. Many terrestrial microwave links use GPS as a timing clock to synchronize TDM (Time Division Multiplexed) traffic. This is especially important on towers with more than one microwave transmitter. Killing the GPS signal could kill a host of other applications relying on said microwave links. Broadcast studios are dependent on GPS timing to co-ordinate television frames per second, when to switch to commercials, etc. There are probably millions of GPS systems that are used soley as a stable clock source rather than a locating device.

“… we have a proposal for a system that has the potential to disrupt GPS reception, perhaps in large areas. Now, do you really think the FCC would approve such a system?”

As a matter of fact, yes I do. They have shown repeatedly that they do NOT primarily support the interest of the citizenry, and that the businesses with the most lucrative connections get the lions share in any rulings.

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